Conventionally, in daily life or while at work, for example, people may tumble over while walking or fall over by a sudden attack of a disease. In such a case, often they are injured by the impact of the falling. In particular, because elderly people have a reduced level of physical ability, they may easily fall over by a slight step or a mild collision, and if they fall over, the lower back, the thigh, the head, and the like may be injured. Also, for example, epileptics may have an epileptic fit and become unconscious to fall over, so that there is a risk that they are hit hard on their heads by their falling.
As a device to protect the body from such falls, an airbag device for the body is known and the airbag device is adapted to absorb the impact of falls by inflating an airbag when an acceleration detected by an acceleration sensor becomes smaller than a predetermined acceleration and an angular velocity detected by an angular velocity sensor becomes greater than a predetermined angular velocity (For example, see Patent Literature 1.).
In the airbag device, when the body becomes in the same state as free fall by falling over or the like, an acceleration detected by the acceleration sensor becomes smaller than a predetermined acceleration, but if it is determined that the body fell over based on only this, an acceleration may be lower than a predetermined acceleration by actions other than falling over such as jumping or leaping slight steps. Therefore, in addition to this condition, only when an angular velocity is generated in any direction by falling over and an angular velocity detected by the angular velocity sensor becomes greater than a predetermined angular velocity, the airbag is inflated. In this case, because an angular velocity may momentarily become greater than the predetermined angular velocity by an abrupt change in posture, only when the determination condition of falling over continues for a predetermined time period or longer, it is determined that the body fell over. As a result, malfunctions are reduced.